\partopsep: extra space added to \topsep when environment starts a new paragraph.

\itemsep: space between successive items.

In the above code the parameters are set locally. If you want, you can make them global with the help of \setlist[enumerate]{topsep=0pt,itemsep=-1ex,partopsep=1ex,parsep=1ex}. For details, refer the enumitem manual at texdoc.

How can I use this approach to affect whole document?
– 71GASep 11 '15 at 17:20

If you replace all enumerates in the document with tight_enumerate it should work out. If you don't want to do that you can also use \renewenvironment{enumerate} instead to overwrite the original enumerate settings (for this document)
– MichielSep 21 '15 at 8:52

I think this is correct way of doing it. In my case, I only wanted to modify enumerate for only specific list not all.
– Joarder KamalSep 21 '15 at 20:51